This does seem related to the 6.10 distro and/or firefox version that is included. I have upgraded to 7.04(Feisty) and do not have the crash problem now, although I still can't get Quicktime files to play in the browser.

In upstream glibc, those bugs are fixed with version 2.8. In Debian, 2.7-11 has the backported fixes. I have not been able to test on Ubuntu yet, but I assume this means the bug is in all versions before Intrepid.